Sounds very useful. I'd love to see them. You could post them to the hardware interfacing board or in the Arduino playground.

In general, yes, new commands that get added to the language (and thus the standard Arduino library) add to the program size. In the future, thanks to some work by nrolland and Don Cross, it will only do so if you actually use the functions in your sketch. We're still careful about what we add to the core language, however, because we want to keep it simple.